This invention relates generally to coating thickness measuring devices, and more particularly to an improved coating thickness measuring device utilizing radiation, such as beta backscatter, for the measurement of coating thicknesses, and is especially suitable for use with small electronic connectors and in other applications where small parts include thin coatings, the thickness of which must be accurately measured.
Various types of coatings are commonly applied to small electronic parts such as connectors, contacts for connectors, and the like. Because if the critical nature of the coating thickness in such applications, it is necessary that the thickness be determined with a high degree of precision. The use of beta radiation backscatter has been found to provide the necessary degree of precision required for the accurate measurement of such thicknesses. As a consequence, several devices have been developed to apply the beta radiation backscatter technique to the measurement of coating thicknesses on various types of electronic parts, such as, for example, on printed circuit boards, and also in other applications. For example, U.S. Pat. No. 3,529,158 shows one type of portable probe in which a base member receives a guide for aligning the member with the area to be measured, the guide then being removed from the member and replaced by a measuring head. U.S. Pat. No. 3,720,833 shows another type of portable probe in which a spring biased locator carried by the probe housing is retracted within the housing by a cam arrangement in response to the lowering of a measuring probe unit into engagement with the workpiece.
Most frequently, the devices which have been developed and commercially marketed involve the manual positioning of the sensing element with respect to the part to be measured. Where extremely small and fragile parts are involved, such as very small connectors or contacts for connectors, it is possible for an unskilled operator of such a measuring device to bring excessive force to bear between the sensing head and the part being measured, with a possible result that the part itself is in some way deformed or damaged or, because of varying contact pressures between the sensing element and the parts from one operator to another, inconsistent readings are obtained.
It is an object of the present invention to overcome the above-described shortcomings of the prior art devices and to provide an improved coating thickness measuring device incorporating a radioactive isotope source and detector and which is adapted to prevent damage to the parts being measured and also to permit repeatable, accurate readings indicative of the coating thickness, which readings are consistent and are independent of the skill and care exercised by the operator.
It is a further object of the invention to provide an improved positioning arrangement by means of a part positioning fixture in which the part can be readily and accurately positioned relative to the probe, so that once the device is set up, parts of the same configuration can be rapidly measured without the need to individually reposition each part for measurement.